Which food? Totally bamboozled!

I'm new to the forum but am hoping to get some good advice on what cat food to go for.

I currently have an older cat, Tinker Bell, who I adopted 2 and a half years ago when she was 10 and in 2 days time we'll be welcoming our kitten Pixie.

In all the preparation for getting Pixie I've discovered that there's a lot more to cat nutrition than I realised. I've always known the main brands were not good and so they are banned in our house. Instead we went for supermarket own brand thinking it was healthier but I realise now that's still not the best diet.

I've since started reading into the various options and have got myself so confused my head is spinning from it all!

I've tried to look at the nutritional attributes for each food but not sure if I'm looking at the right bits or for the right kind of values. So far I think I've narrowed it down to:

Nature's Menu Lily's Kitchen Thrive

I've also found in Sainsbury's today 'Naturo' so I've tried that with Tinker Bell and it's gone down well!

My main queries I'd like advice on are:

What should I be looking for when comparing different foods?

Can the cat and kitten be fed on the same good quality food or do they need separate diets?

What are the best foods to balance price and quality? Obviously with 2 mouths to feed money has to be an object but we are willing to pay a bit extra if it's going to be better for them.

Sorry this has ended up a long post, am looking forward to all the helpful advice to hopefully de-fuzz my brain!